Under tendency to reduce the amount of emission of carbon dioxide that promotes global warming, and in recent/current situation in which bright LEDs with high luminous efficiency are realized, low-power LEDs (light emitting diodes, semiconductor optical sources) are beginning to be popular also as optical sources of lamp devices for in-vehicle use, in place of conventional tungsten filament-based light bulbs. These LEDs are long-life and can produce stable brightness under easy control that makes constant a current supplied thereto, and are thus, well-suited as optical sources of lamp devices for in-vehicle use. Thus, also with the help of recent increase in output power (luminance intensity), they are beginning to be popular also as optical sources of the headlights for in-vehicle use.
Meanwhile, the optical systems of the headlights for in-vehicle use are classified to: a parabolic type in which a concave mirror reflector is used and the light emitted by an optical source is reflected by the mirror reflector so as to go out ahead of the vehicle; and a projector type in which a convex projection lens is used and the light emitted by an optical source is refracted by the projection lens so as to go out ahead of the vehicle.
In the followings, supplemental description will be made about configurations of the projector-type headlights for in-vehicle use that are related to the invention of this application.
In a conventional configuration that uses a tungsten filament as an optical source, lead wires are connected to both ends of the filament with a length of about 4 mm that radiates light all around, and in addition, a glass bulb exists outward of the filament. Thus, it is unable to arbitrarily modify the shape of a light emitting portion or the light radiation direction.
For that reason, a spheroidal mirror reflector is used and a filament serving as an optical source is placed at one focal point of the spheroidal mirror reflector, so that the light emitted by the filament is converged at the other focal point to thereby form a real image of the filament. Since no structural object exists near the real image of the filament, an arbitrary optical member can be used there, so that a light distribution for passing light for in-vehicle use that illuminates the front of a vehicle is formed by projecting ahead of the vehicle a necessary portion in the light that passes through the real image of the filament. That is to say, a light shielding plate is placed near the real image of the filament, so that unwanted light is blocked by the light shielding plate to thereby form a dark portion that is essential for passing light so as not to illuminate the driver of an oncoming vehicle. Namely, when an optical source is the filament in a state covered by the glass bulb without change, it is unable to be used as an optical source that radiates a light distribution for passing light. Thus, such a configuration is applied in which the real image of the filament around which no structural object exists is forcibly formed using the spheroidal mirror reflector, and the real image of the filament is subjected to shape modification, and then guided into the projection lens.
However, with respect to a projector-type headlight for in-vehicle use in which the above-described LED is used as an optical source, a light emitting portion, that is, a light emitting face of the LED can be formed into an arbitrary shape, and no glass bulb exists outward. Thus, it is also allowable to place a member for adjusting the light distribution near the LED. Namely, with respect to the projector-type headlight for in-vehicle use in which the LED is used as an optical source, it is unnecessary to follow the conventional optical system and light distribution technology in which a tungsten filament is used.
In the followings, examples will be described about the headlight for in-vehicle use that does not use a conventional spheroidal mirror reflector even though it is a projector type, and that is configured so that the light-emitting face of the LED is directed ahead of the vehicle and the light emitted by the LED is made directly incident on the projection lens.
A direct-projection type lamp device for illumination according to Patent Document 1 is configured so that, in the light emitted by the LED, widely-spread light that is non-incident on a projection lens is recovered using an auxiliary lens placed around the LED. Because of the use of the auxiliary lens, the light-beam utilization rate can be enhanced.
However, since it is configured so that the light that is non-incident on the projection lens is guided ahead of the vehicle while bypassing the projection lens, the auxiliary lens that is larger than the aperture of the projection lens is used. As the result, the opening portion of the lamp device is larger, so that the device is not suited as a compact headlight or optical member.
A lamp unit for vehicle according to Patent Document 2 is configured with a light-scattering optical face provided at the rear focal point of a projection lens in order to mitigate unevenness (illuminance unevenness) of light emitted by an LED optical source composed of a plurality of LEDs, wherein light emitted by each of the LEDs is caused to pass through the optical face to be combined together, and is then guided into the projection lens. The illumination light having been projected through scattering by that lens face, becomes optically uniform.
For example in FIG. 1, etc. of Patent Document 2, there is illustrated a configuration in which a projection lens (20) is composed of a plurality of lenses (21, 22); a face (S1) of the lens (21) closest to an optical source unit (30) is formed into a shape for scattering light; and this lens face (S1) is placed to be matched to the rear focal point of the projection lens (20).
Further, for example in FIG. 5, FIG. 6, etc. of Patent Document 2, there is illustrated a configuration in which a cylindrical light guide member (32) whose inside serves as a reflection face (31a) is provided between the projection lens (20) and the optical source unit (30); the face (S1) of the lens (21) closest to the optical source unit (30) is formed into a shape for scattering light; and an outlet port (31c) of the light guide member (32), the lens face (S1) for scattering light, and the rear focal point of the projection lens (20) are matched to the same position.
In the foregoing, the numerals in the parentheses are cited from those in Patent Document 2.
Because the surface of the projection lens is formed into a light-scattering shape as described above, it is possible to make uniform brightness produced by the respective LEDs; however, when the configuration in Patent Document 2 is used for passing light for in-vehicle use, a boundary between the upper dark portion and the lower light portion for passing light will be blurred due to the presence of the scattering face. Thus, this configuration is not suited for passing light that requires clear lightness and darkness in the upper and lower sides.
A headlight for vehicle according to Patent Document 3 is configured with a first reflection face being a planer face and a second reflection face being a curved face that are placed in the upper side and the lower side, respectively, so that an optical axis of an LED is sandwiched between them, wherein a short side of the first reflection face is matched to the focal point group of a projection lens.
For example in FIG. 8, etc. of Patent Document 3, there is illustrated an optical member (16B) in which a portion surrounded by the first reflection face (22) and the second reflection face (26) is filled with a resin (36). The light emitted by an LED optical source (12) is guided into a projection lens (14) while being reflected on the first and second reflection faces (22, 26), so that the utilization rate of the LED optical source (12) can be enhanced and a thin lamp device with a short depth can be configured (the numerals in the parentheses are cited from those in Patent Document 3).
However, the first and second reflection faces have to be subjected to surface treatment for reflection. Namely, each reflection face to be used is required to be mirror face, and in order to form such a reflection mirror, a plurality of processes, for example, a vapor deposition of a metal for reflection, an antioxidant treatment of the vapor deposited face, and the like become necessary. Accordingly, its unit price as a component rises. Further, because of the use of a plurality of components, the configuration becomes complex, so that there may also be a possibility that the assembly man-hours increase.